In a conventional art, in HSDPA (High-Speed Downlink Packet Access) of 3GPP, adaptive modulation where the modulation scheme is adaptively controlled according to propagation path conditions and scheduling for transmitting a user signal for which propagation path conditions are comparatively superior have been employed in downlink high-speed packet transmission.
In multi-carrier transmission such as OFDM and MC-CDMA (for example, Hara, Kawabata, Duan and Sekiguchi, “MC-CDM System for Packet Communications Using Frequency Scheduling”, TECHNICAL REPORT OF IEICE, RCS2002-129, July 2002, refer to pp. 61-66) being examined as transmission schemes for beyond 3G mobile communication systems, high speed transmission is implemented using a large number of sub-carriers.
In this kind of transmission scheme, performing adaptive modulation and scheduling every sub-carrier is examined.
With this kind of adaptive modulation and scheduling system, it is necessary for the mobile station to give reporting of channel quality information (CQI (Channel Quality Indicator)) of each sub-carrier instantaneously at a base station.
The mobile station reports individual CQI's on every sub-carrier for all sub-carriers to the base station.
A base station then determines the sub-carrier, modulation scheme and encoding rate to be used at each mobile station in accordance with a predetermined scheduling algorithm taking into consideration the CQI's from each mobile station.
Typically, sub-carriers with comparatively good propagation path conditions are allocated to each mobile station, and a modulation scheme and encoding rate satisfying a predetermined packet error rate are employed for these propagation conditions.
In the event that a base station transmits to a plurality of mobile stations at the same time, frequency scheduling is carried out using CQI's of all of the sub-carrier from all of the users.
In other words, if there are 64 sub-carriers, it is necessary for each mobile station to give reporting of 64 CQI's.
In this event, when a CQI is expressed using five bits, it is necessary to transmit a total of 64×5=320 bits per one user in each wireless frame.
However, with wireless communication apparatus of the conventional art, the quantity of signal required for CQI reporting is enormous. This means that interference incurred by other data channels and other cells is large, and the quantity of data that can be transmitted is therefore substantially reduced.
Further, as the quantity of signal for giving CQI reporting is enormous, power consumption of the mobile station is increased and a battery life is shortened.